1. Field of the Invention
The present invention relates to an image forming device, a position shift correction method, and a recording medium.
2. Description of the Related Art
In the related art, a color image forming device such as a laser printer includes a color image forming device of a tandem system in which an image of each color formed by a unit of each of the colors is superimposed on an intermediate transfer belt, and then, the image on the intermediate transfer belt is transferred onto a sheet.
In such a color image forming device of a tandem system, resist correction processing of accurately matching an image position of each of the colors is performed. For example, in the resist correction processing, the color image forming device forms an image of a patch pattern (hereinafter, referred to as a “patch image”) such as an oblique line or a horizontal line for detecting a shift of a transfer position in a main scanning direction and a sub-scanning direction on the transfer belt for each of the colors. After that, in the resist correction processing, the color image forming device reads the interval between the respective patch images to calculate a color shift correction amount, and corrects a color shift in the main scanning direction and the sub-scanning direction of each of the colors.
Recently, in the color image forming device of the tandem system, there is a case where an intermediate transfer belt of an elastic body (hereinafter, referred to as an “elastic belt”) is used in order to respond to various recording media (for example, uneven paper and the like). Regular reflection light extremely decreases on such an elastic belt. For this reason, in a patch image detection system using regular reflection, a secondary transfer belt using a material from which regular reflection light can be obtained is also used in addition to the elastic belt. That is, in a case where the elastic belt and the secondary transfer belt are used, the color image forming device transfers the patch image which is transferred onto the elastic belt to the secondary transfer belt, and reads the patch image on the secondary transfer belt by a regular reflection sensor.
When a color image is transferred onto the secondary transfer belt as described above (secondary transfer), in the color image forming device of the tandem system, the patch image is transferred onto the secondary transfer belt in optimal conditions (a transfer voltage or a transfer current) at the time of printing the color image, in consideration of superimposing color images of at least two or more colors.
Here, the patch image of each of the colors formed on the intermediate transfer belt is transferred in optimal primary transfer conditions in each of the colors, and thus, is accurately transferred onto the intermediate transfer belt.
In contrast, in the secondary transfer, the transfer of the patch image is set in the optimal conditions as the color image, and thus, there is a case where the transfer of the patch image on the secondary transfer belt is not optimal according to the shape or the color of the patch image. In such a case, there is a problem in which the transfer onto the secondary transfer belt is insufficient, and a variation or a deviation occurs in an adhesion amount of a toner or an ink. In particular, such a problem is remarkable with respect to a black color.
Thus, in a case where the variation or the deviation occurs in the adhesion amount, the output sensed by the regular reflection sensor becomes unstable, or the phase of the output sensed by the regular reflection sensor is shifted. The unstable output or the phase shift becomes an error in reading the interval between the patch images, and thus, it is not possible to detect an accurate position shift. Thus, in a case where the accurate position shift is not capable of being detected, the color image forming device of the tandem system sets an incorrect adjustment value, and thus, there is a problem in which color matching is not capable of being performed.